This application is related to Disclosure Document No. 425,240, filed Oct. 7, 1997. It is understood that this Document will be placed in and become a part of the file wrapper of this application.
This application relates in general to display devices and, in particular, to a display employing an improved structure for grid electrodes so that the grid electrodes may be kept in precise position.
In image display devices such as a color television, a mask and electrical potentials applied thereto are used for controlling the paths of electrons directed towards particular pixel locations on the television screen despite temperature changes. Therefore, it is important to maintain the position of a mask in precise alignment relative to pixel positions on the phosphor layer. Thus, U.S. Pat. No. 4,308,485, for example, discloses a mask made of a thin metallic plate having an edge fixed to a profiled metallic frame having the general shape of an angle iron with two branches. The edge of the mask is fixed onto one branch of the frame and the other branch of the frame is attached to the inner surface of the front part of the color television tube. It is stated that, dilatations of the mask are absorbed by the edges of the mask, where the edges are between bosses, so that temperature variations of the mask have minimal effects on the position of the mask.
U.S. Pat. No. 4,789,805 illustrates another type of shadow mask suspended from the glass envelope of a cathode array tube by spring steel suspension elements which are connected to a glass envelope, such as that in a cathode ray tube, by metal connectors which are plastically deformed at low temperatures to avoid thermal stresses on the glass. Another mechanism for mounting the mask onto a cathode array tube is described in U.S. Pat. No. 5,634,837. In this patent, positioning posts fixed on a back plate and positioning pins extending from a face plate are engaged to align the face and back plates. The shadow mask has openings through which the positioning posts extend so as to position the mask with respect to the back plate.
After a shadow mask has been mounted onto a face plate assembly, a sealing process of the face plate to the funnel of a cathode array tube at high temperature may cause the grid wires in the mask to permanently expand and, therefore, sag. U.S. Pat. No. 5,507,677 discloses a method for pre-stressing the mask so that the grid wires therein will experience only a small additional creep during such high temperature sealing process.
While the above-described mechanisms and methods for maintaining alignment of a mask may be useful for cathode array tube applications, they are usually too bulky and cumbersome for use in flat panel displays. In order to be able to precisely align a mask using the above-described alignment mechanisms, such mechanisms are usually required to be of a certain size. In many flat panel displays, it is desirable to keep the distance between the face and back plates of the display at a small value, typically of the order of several millimeters or less. Given such spacing in a flat panel display, it is impractical to use the above-referenced mounting mechanisms or methods for cathode array tubes. It is, therefore, desirable to provide an improved design for mounting grid electrodes so that these electrodes can be precisely positioned with respect to other elements of the display.
Temperature variations of grid or focusing electrodes may cause the electrodes to expand or contract and, consequently, misalign with respect to the pixels of the display. By causing the grid or focusing electrodes to be under tension that is maintained by means of a rim during the operation of the display, the effect of temperature variations on the alignment of the grid electrodes is much reduced. Therefore, one aspect of the invention is directed towards an electrode structure where the structure includes a rim and an electrode connected to the rim. The electrode comprises a layer of electrically conductive material that is in tension. The rim causes tension in the layer to be maintained. The electrode structure has a thickness not more than about 10 millimeters, so that when it is placed between an anode or on or near a front face plate and at least one cathode, the distance between the front face plate and a back plate beyond the cathode can be maintained to be quite small; in the preferred embodiment, this distance may be no more than 20 millimeters. When electrical potentials are applied to the anode, the at least one cathode and the layer, electrons are directed to desired portions of a luminescent layer at or near the anode for displaying images.
According to another aspect of the invention, an electrode structure is employed between an anode and at least one cathode. The structure includes a rim and an electrode connected to the rim, where the electrode includes a layer of electrically conductive material under tension. The rim causes tension in the layer to be maintained. The layer and the rim have different thermal coefficients of expansion so that the tension may be maintained despite temperature changes. The front and back plates of the display device are spaced apart by not more than 20 millimeters, so that electrons may be controlled to be directed to precise pixel dot locations for improved resolution. The layer may be used for focusing electrons to desired portions of a luminescent layer at or near the anode for displaying images.
The prior art mounting mechanisms referred to above for cathode array tubes are cumbersome and time consuming. Thus, according to another aspect of the invention, the electrode structure of a flat panel display device has a rim, an electrode connected to the rim, where the electrode includes a layer of electrically conductive material having holes therein for focusing electrons. The rim forms at least a portion of a sidewall structure connected to a face and a back plate to form a sealed vacuum chamber housing an anode and at least one cathode. This flat panel display device is particularly simple to assemble. In one embodiment, once the rim of the electrode structure has been aligned with respect to the front face plate and the back plate in assembly of the sidewall structure with the face and back plates, the layer will be automatically aligned with respect to the front face plate and the back plate. Thus, such method of assembly is much simpler compared to the conventional mounting and alignment processes referred to above for cathode array tubes.
Another aspect of the invention is a method for making a flat panel display. A layer of electrically conductive material having holes therein is formed. The layer is fixed relative to a rim at a temperature above an operating temperature of the display to form an electrode structure. The layer has a thermal coefficient of expansion that is larger than that of the rim. Temperature(s) of the layer and rim is reduced to cause the layer to be under tension. The electrode structure is placed between and aligned with an anode on or near a front face plate and at least one cathode. The position of the electrode structure relative to a front and a back plate is then caused to be set to form a flat panel display device.
Another aspect of the invention is directed to a cathode ray tube display device comprising a front face plate; an anode on or near the front face plate; a first layer of luminescent material on or near the anode; and an electron gun. The electron gun preferably comprises a cathode, a funnel enclosing the cathode and means for deflecting an electron beam from the cathode. An electrode structure is placed between the anode and the cathode, said structure including a rim and an electrode connected to the rim, said electrode comprising a second layer of electrically conductive material under tension, wherein the rim causes tension to be maintained in said second layer, said electrode structure having a thickness not more than about 10 millimeters. When electrical potentials are applied to the anode, the second layer, the cathode and the deflecting means, electrons from the cathode are caused to reach desired portions of the luminescent layer for displaying images.